Proof: Make the above picture, PQ,? Public relations? The location of ladders on different walls.

According to the chart, it is easy to get ∠ qpr = 60.

Because the step length is constant, that is, PQ=PR.

So △QPR is an equilateral triangle? (An isosceles triangle with a 60-degree angle is an equilateral triangle)

? So QR=PR

Make RD perpendicular to? QD。

? Because it was concluded? ∠DQR=？ 75

? So RD=n

? And because the two walls are parallel, RD is parallel to the ground, which is equal according to the parallel lines.

Get RD=m?

? So what? M=n (equivalent substitution)